Citation style

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Citation style used at Citizendium is discussed specifically at CZ:citation style

Scholarly and technical publications use many different formats for citing previously published work in their articles.

A citation allows the reader to verify a statement made in the text, to see the source of data, to gain more statistical detail, or to explore the original context of a quoted passage. Often, the text is marked with a superscripted number[1] just after the section to which the citation is most relevant, or at the end of the relevant paragraph, where there may be more that one source indicated.[2]

The superscripted mark may be a numeral, a Roman numeral, or a letter. Alternatively, the citation may take the form of naming the main authors of the cited reference source, along with a date, in parentheses. This approach is used in the Harvard style (also known as the author-date style). An example of an in-text citation would therefore be: (Smith, 1997). Variants of this approach use a letter as suffix if the same author is cited but for different articles published in the same year. For example (Jones, 1997a), if Jones is cited for more than one 1997 article. Another variant permits the grouping of multiple authors with distinct publications which were produced in the same year: (Smith and Jones, 2000), and (Timorof et al. 1927). Et al. is an abbreviation for et alia, meaning 'and others' in Latin, which is usually used if there are more than three named authors for a particular publication.

With word processing programs, it is easy to develop automatically generated, correctly numbered citations in documents. In some publications, citations are included in the footnotes on each page. Precise attention to the format and consistency of citations and other bibliographic information is expected in professional quality manuscripts.

Examples of citation styles

Here are three examples of citations from Proceedings of the National Academy of Sciences, USA, a well respected scientific journal (often called just PNAS by scientists).

1. Neuhaus J-M, Sitcher L, Meins F, Jr, Boller T (1991) A short C-terminal sequence is necessary and sufficient for the targeting of chitinases to the plant vacuole. Proc Natl Acad Sci USA 88: 10362-10366.
2. Kellert S (1996) The Value of Life: Biological Diversity and Human Society (Island Press, Washington, DC), 2nd Ed, pp 13-34.
3. Hill AVS (1991) in Molecular Evolution of the Major Histocompatibility Complex, eds Klein J, Klein D (Springer, Heidelberg), pp 403-420.

Citation 1 is a journal article citation, 2 is a book citation, and 3 is a book chapter citation.

In Molecular Biology and Evolution, the in-text citation style is like this: (Lake et al. 1984; Woese and Olsen 1986), and in the endnotes the citations are listed like this:

BALDACCI, B., F. GUINET, J. TILLIT, G. ZACCAI, and A.-M. DE RECONDO. 1990. Functional
implications related to the gene structure of the elongation factor EF-Tu form Halobacterium
marismortui. Nucleic Acids Res. 18:507-511.

The system for providing page numbers is different from PNAS USA, and the author's names are capitalized. Interestingly, 'form' in the citation is a typographical error ( here for the original paper).

In short, many different citation styles are used today in scholarly literature.

How can authors work out how to cite publications correctly

A guide for how to provide citation details is provided to prospective authors by each scholarly publication. One accessible example is from the internet publication Public Library of Science Biology (PLoS Biology), an Open Access journal. They give the following guidelines for submitted manuscripts:

"PLoS uses the numbered citation (citation-sequence) method. References are listed and numbered in the order that they appear in the text. In the text, citations should be indicated by the reference number in brackets. Multiple citations within a single set of brackets should be separated by commas. Where there are more than three sequential citations, they should be given as a range. ... For all references, list the first five authors; add "et al." if there are additional authors. You can include a DOI number for the full-text article as an alternative to or in addition to traditional volume and page numbers. Please use the following style for the reference list:

Published Papers

1. Sanger F, Nicklen S, Coulson AR (1977) DNA sequencing with chain-terminating inhibitors. Proc Natl Acad Sci U S A 74: 5463–5467.

Accepted Papers

Same as above, but "In press" appears instead of the page numbers. Example: Adv Clin Path. In press.

Electronic Journal Articles

1. Loker WM (1996) "Campesinos" and the crisis of modernization in Latin America. Jour Pol Ecol 3. Available: Accessed 11 August 2006.


1. Bates B (1992) Bargaining for life: A social history of tuberculosis. Philadelphia: University of Pennsylvania Press. 435 p.

Book Chapters

1. Hansen B (1991) New York City epidemics and history for the public. In: Harden VA, Risse GB, editors. AIDS and the historian. Bethesda: National Institutes of Health. pp. 21–28."

(End of direct quote from PLoS Biology)

Abbreviations and their meaning

Journal abbreviations

Types of bibliographic information


Electronic publications and hyper-linked citation resources



  1. An unambiguous direction to the source of the information is supplied here.
  2. Source 1.
    • Source 2.
    • Source 3. (This is what we are doing in many Citizendium biology pages to make the text less cluttered).